Comparative Analysis Of Endophytic Bacteria Communities In Two Ecotypes Of Sedum Alfredii

Obvious differences of the ability of accumulation of heavy metals were observed in hyperaccumulator ecotype and non-hyperaccumulator ecotype of S.alfredii, but little is known about the difference of its associated endophytic bacteria community. Therefore this paper first use cultural method to compare the number of cultural bacteria in rhizosphere soil, roots, stems and leaves,isolated and purified representative strains, and measured the zinc and cadmium resistance levels, secretion of indole acetic acid, siderophere and dissolved inorganic phosphorus characteristics. A further 4-months pot experiment were conducted to evaluate the sustainable impacts of cadmium gradients on endophytic bacterial diversity and community composition in two ecotypes of S.alfredii growing at agricultural soil. Effectes of soil chemical properties, plant growth characteristics, cadmium concentration in leaves, stems, roots on the community structures and biological roles of endophytic bacteria of two ecotypes of S.alfredii were also researched by Redundancy analysis(RDA) based on the relative abundance of bacterial genus. The research aims at explaining the physiological and ecological mechanisms of cadmium uptake, detoxification, accumulation in hyperaccumulator ecotype of S.alfredii from the aspect of soil-plant-endophytes interaction. The main results of this research were as follows:(1)A large number of cultural bacteria were found in leaves, stems, roots and rhizosphere of hyperaccumulator ecotype of S.alfredii growing at a Pb/Zn mine of Quzhou in Zhejiang and non-hyperaccumulator ecotype of S.alfredii growing at tea garden of Jiuxi in Zhejiang through traditional bacterial isolation and cultural techniques. In this study, a total of 30 endophytic bacteria were isolated from the leaves, stems and roots of hyperaccumulator ecotype of S.alfredii and 32 endophytic bacteria were isolated from non-hyperaccumulator ecotype of S.alfredii. The population density of endophytic bacteria of leaves and roots of hyperaccumulator ecotype S.alfredii were significantly higher than that in non-hyperaccumulator ectype of S.alfredii, whereas the contrast were for the stems. In the endophytes of hyperaccumulator ecotype of S.alfredii and the non-hyperaccumlator ecotype of S.alfredii, the proportion of resistance of Zn?5 mmol·L-1, resistance of Cd?0.5 mmol·L-1, production of indole- 3- acetic-acid(IAA)?15 mg·L-1, siderophore activity unit?20 and the diameter of mineral phosphorus solubilizing circle?2 mm were 43.33% and 12.50%?36.67% and 18.75%?25.00% and 50.00%?87.50% and 16.67%?71.43% and 100% respectively.(2)With the increasing Cd concentration of agriculture soil, in the hyperaccumulator ecotype of S.alfredii, the number of endophytic bacteria in leaves were decreasing, which in stems were increasing and which in roots were first increasing and then decreasing, while in the leaves, stems and roots tissue of non-hyperaccumulator ecotype of S.alfredii were all decreasing.(3)High-throughput sequencing results showed that there were diverse endophytic bacteria in the leaves, stems and roots tissues of two ecotypes of S.alfredii. The most heavily sequenced endophytic bacteria in S.alfredii were related to Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes which were the most abundant phylum in all samples. At the genus level, the dominant endophytic bacteria in hyperaccumulator ecotype of S.alfredii were Streptococcus, Sphingomonas, Neisseria, Novosphingobium and Rothia, while in non-hyperaccumulator ecotype of S.alfredii were Bacteroide, Sphingomonas, Methylobacterium, Clostridium, Bacillus and Rhodococcus. Streptococcus, Neisseria, Rothia, Novosphingobium and Bifidobacterium were dominant endophytic bacteria in the control treatment, whereas Sphingomonas, Sphingobacterium, Enterococcus, Methylobacterium, Bradyrhizobium, Prevotella, Streptomyces and Ralstonia were dominant endophytic bacteria in the treatment with increasing cadmium concentration.(4) Redundancy analysis(RDA) showed that the genetic diversity of endophytic bacterial community structures were affected by Cd content in plant tissues, Ca Cl2 extractable Cd concentration in rhizosphere soil of S.alfredii, soil pH, shoot height, fresh weight and dry weight of plant. The relative abundance of Sphingomonas was mainly affected by Cd content in leaves; in stems, Sphingobacterium, Pseudomonas and Enterococcus were shown to be positively related to Cd concentration of stems; in leaves, Veillonella, Klebsiella and Bacteroides were related to shoot height and leaves fresh weight; in roots, Phyllobacterium, Methylobacterium and Bradyrhizobium were related to Soil Cd and Cd concentration, Clostridium and Rhizobium were related to soil pH.